java.util.regex
Class Pattern

java.lang.Object
  java.util.regex.Pattern

All Implemented Interfaces:

Serializable

public final class Pattern
extends Object
implements Serializable

Represents a pattern used for matching, searching, or replacing strings. Patterns are specified in terms of regular expressions and compiled using an instance of this class. They are then used in conjunction with a Matcher to perform the actual search.

A typical use case looks like this:

 Pattern p = Pattern.compile("Hello, A[a-z]*!");
  
 Matcher m = p.matcher("Hello, Android!");
 boolean b1 = m.matches(); // true
  
 m.setInput("Hello, Robot!");
 boolean b2 = m.matches(); // false
 

The above code could also be written in a more compact fashion, though this variant is less efficient, since Pattern and Matcher objects are created on the fly instead of being reused. fashion:

     boolean b1 = Pattern.matches("Hello, A[a-z]*!", "Hello, Android!"); // true
     boolean b2 = Pattern.matches("Hello, A[a-z]*!", "Hello, Robot!");   // false
 

Please consult the package documentation for an overview of the regular expression syntax used in this class as well as Android-specific implementation details.

Since:

Android 1.0

See Also:

Matcher, Serialized Form

Field Summary

static int	CANON_EQ This constant specifies that a character in a Pattern and a character in the input string only match if they are canonically equivalent.
static int	CASE_INSENSITIVE This constant specifies that a Pattern is matched case-insensitively.
static int	COMMENTS This constant specifies that a Pattern may contain whitespace or comments.
static int	DOTALL This constant specifies that the '.' meta character matches arbitrary characters, including line endings, which is normally not the case.
static int	LITERAL This constant specifies that the whole Pattern is to be taken literally, that is, all meta characters lose their meanings.
(package private) int	mGroupCount Holds the number of groups in the pattern.
(package private) int	mNativePattern Holds a handle (a pointer, actually) for the native ICU pattern.
static int	MULTILINE This constant specifies that the meta characters '^' and '$' match only the beginning and end end of an input line, respectively.
static int	UNICODE_CASE This constant specifies that a Pattern is matched case-insensitively with regard to all Unicode characters.
static int	UNIX_LINES This constant specifies that a pattern matches Unix line endings ('\n') only against the '.', '^', and '$' meta characters.

Method Summary

static Pattern	compile(String pattern) Compiles a regular expression, creating a new Pattern instance in the process.
static Pattern	compile(String pattern, int flags) Compiles a regular expression, creating a new Pattern instance in the process.
protected void	finalize() Called by the virtual machine when there are no longer any (non-weak) references to the receiver.
int	flags() Returns the flags that have been set for this Pattern.
Matcher	matcher(CharSequence input) Returns a Matcher for the Pattern and a given input.
static boolean	matches(String regex, CharSequence input) Tries to match a given regular expression against a given input.
String	pattern() Returns the regular expression that was compiled into this Pattern.
static String	quote(String s) Quotes a given string using "\Q" and "\E", so that all other meta-characters lose their special meaning.
String[]	split(CharSequence input) Splits a given input around occurrences of a regular expression.
String[]	split(CharSequence inputSeq, int limit) Splits the given input sequence around occurrences of the Pattern.
String	toString() Returns a string containing a concise, human-readable description of the receiver.

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

UNIX_LINES

public static final int UNIX_LINES

This constant specifies that a pattern matches Unix line endings ('\n') only against the '.', '^', and '$' meta characters.

Since:

Android 1.0

See Also:

Constant Field Values

CASE_INSENSITIVE

public static final int CASE_INSENSITIVE

This constant specifies that a Pattern is matched case-insensitively. That is, the patterns "a+" and "A+" would both match the string "aAaAaA".

Note: For Android, the CASE_INSENSITIVE constant (currently) always includes the meaning of the UNICODE_CASE constant. So if case insensitivity is enabled, this automatically extends to all Unicode characters. The UNICODE_CASE constant itself has no special consequences.

Since:

Android 1.0

See Also:

Constant Field Values

COMMENTS

public static final int COMMENTS

This constant specifies that a Pattern may contain whitespace or comments. Otherwise comments and whitespace are taken as literal characters.

Since:

Android 1.0

See Also:

Constant Field Values

MULTILINE

public static final int MULTILINE

This constant specifies that the meta characters '^' and '$' match only the beginning and end end of an input line, respectively. Normally, they match the beginning and the end of the complete input.

Since:

Android 1.0

See Also:

Constant Field Values

LITERAL

public static final int LITERAL

This constant specifies that the whole Pattern is to be taken literally, that is, all meta characters lose their meanings.

Since:

Android 1.0

See Also:

Constant Field Values

DOTALL

public static final int DOTALL

This constant specifies that the '.' meta character matches arbitrary characters, including line endings, which is normally not the case.

Since:

Android 1.0

See Also:

Constant Field Values

UNICODE_CASE

public static final int UNICODE_CASE

This constant specifies that a Pattern is matched case-insensitively with regard to all Unicode characters. It is used in conjunction with the CASE_INSENSITIVE constant to extend its meaning to all Unicode characters.

Note: For Android, the CASE_INSENSITIVE constant (currently) always includes the meaning of the UNICODE_CASE constant. So if case insensitivity is enabled, this automatically extends to all Unicode characters. The UNICODE_CASE constant then has no special consequences.

Since:

Android 1.0

See Also:

Constant Field Values

CANON_EQ

public static final int CANON_EQ

This constant specifies that a character in a Pattern and a character in the input string only match if they are canonically equivalent. It is (currently) not supported in Android.

Since:

Android 1.0

See Also:

Constant Field Values

mNativePattern

transient int mNativePattern

Holds a handle (a pointer, actually) for the native ICU pattern.

mGroupCount

transient int mGroupCount

Holds the number of groups in the pattern.

Method Detail

compile

public static Pattern compile(String pattern)
                       throws PatternSyntaxException

Compiles a regular expression, creating a new Pattern instance in the process. This is actually a convenience method that calls compile(String, int) with a flags value of zero.

Parameters:

pattern - the regular expression.

Returns:

the new Pattern instance.

Throws:

PatternSyntaxException - if the regular expression is syntactically incorrect.

Since:

Android 1.0

compile

public static Pattern compile(String pattern,
                              int flags)
                       throws PatternSyntaxException

Compiles a regular expression, creating a new Pattern instance in the process. Allows to set some flags that modify the behavior of the Pattern.

Parameters:

pattern - the regular expression.

flags - the flags to set. Basically, any combination of the constants defined in this class is valid.

Note: Currently, the CASE_INSENSITIVE and UNICODE_CASE constants have slightly special behavior in Android, and the CANON_EQ constant is not supported at all.

Returns:

the new Pattern instance.

Throws:

PatternSyntaxException - if the regular expression is syntactically incorrect.

Since:

Android 1.0

See Also:

CANON_EQ, CASE_INSENSITIVE, COMMENTS, DOTALL, LITERAL, MULTILINE, UNICODE_CASE, UNIX_LINES

pattern

public String pattern()

Returns the regular expression that was compiled into this Pattern.

Returns:

the regular expression.

Since:

Android 1.0

flags

public int flags()

Returns the flags that have been set for this Pattern.

Returns:

the flags that have been set. A combination of the constants defined in this class.

Since:

Android 1.0

See Also:

CANON_EQ, CASE_INSENSITIVE, COMMENTS, DOTALL, LITERAL, MULTILINE, UNICODE_CASE, UNIX_LINES

matcher

public Matcher matcher(CharSequence input)

Returns a Matcher for the Pattern and a given input. The Matcher can be used to match the Pattern against the whole input, find occurrences of the Pattern in the input, or replace parts of the input.

Parameters:

input - the input to process.

Returns:

the resulting Matcher.

Since:

Android 1.0

matches

public static boolean matches(String regex,
                              CharSequence input)

Tries to match a given regular expression against a given input. This is actually nothing but a convenience method that compiles the regular expression into a Pattern, builds a Matcher for it, and then does the match. If the same regular expression is used for multiple operations, it is recommended to compile it into a Pattern explicitly and request a reusable Matcher.

Parameters:

regex - the regular expression.

input - the input to process.

Returns:

true if and only if the Pattern matches the input.

Since:

Android 1.0

See Also:

compile(java.lang.String, int), Matcher.matches()

split

public String[] split(CharSequence input)

Splits a given input around occurrences of a regular expression. This is a convenience method that is equivalent to calling the method split(java.lang.CharSequence, int) with a limit of 0.

Parameters:

input - the input sequence.

Returns:

the resulting array.

Since:

Android 1.0

split

public String[] split(CharSequence inputSeq,
                      int limit)

Splits the given input sequence around occurrences of the Pattern. The function first determines all occurrences of the Pattern inside the input sequence. It then builds an array of the "remaining" strings before, in-between, and after these occurrences. An additional parameter determines the maximal number of entries in the resulting array and the handling of trailing empty strings.

Parameters:

inputSeq - the input sequence.

limit - Determines the maximal number of entries in the resulting array.

• For n > 0, it is guaranteed that the resulting array contains at most n entries.
• For n < 0, the length of the resulting array is exactly the number of occurrences of the Pattern +1. All entries are included.
• For n == 0, the length of the resulting array is at most the number of occurrences of the Pattern +1. Empty strings at the end of the array are not included.

Returns:

the resulting array.

Since:

Android 1.0

quote

public static String quote(String s)

Quotes a given string using "\Q" and "\E", so that all other meta-characters lose their special meaning. If the string is used for a Pattern afterwards, it can only be matched literally.

Parameters:

s - the string to quote.

Returns:

the quoted string.

Since:

Android 1.0

toString

public String toString()

Description copied from class: Object

Returns a string containing a concise, human-readable description of the receiver.

Overrides:

toString in class Object

Returns:

String a printable representation for the receiver.

finalize

protected void finalize()

Description copied from class: Object

Called by the virtual machine when there are no longer any (non-weak) references to the receiver. Subclasses can use this facility to guarantee that any associated resources are cleaned up before the receiver is garbage collected. Uncaught exceptions which are thrown during the running of the method cause it to terminate immediately, but are otherwise ignored.

Note: The virtual machine assumes that the implementation in class Object is empty.

Overrides:

finalize in class Object